Re: Reducing tuple overhead

On 4/25/15 12:12 AM, Amit Kapila wrote:
> > ... which isn't possible. You can not go from a heap tuple to an
> index tuple.
>
> We will have the access to index value during delete, so why do you
> think that we need linkage between heap and index tuple to perform
> Delete operation? I think we need to think more to design Delete
> .. by CTID, but that should be doable.

The problem with just having the value is that if *anything* changes
between how you evaluated the value when you created the index tuple and
when you evaluate it a second time you'll corrupt your index. This is
actually an incredibly easy problem to have; witness how we allowed
indexing timestamptz::date until very recently. That was clearly broken,
but because we never attempted to re-run the index expression to do
vacuuming at least we never corrupted the index itself.

> > This has been discussed in the past.
>
> I have tried to search in archive, but not getting what is the exact
> problem.

Unfortunately I can't find prior discussion now either... :/
--
Jim Nasby, Data Architect, Blue Treble Consulting
Data in Trouble? Get it in Treble! http://BlueTreble.com